The invention relates to combination ovens generally and more particularly to a windowed door assembly for a combination microwave and hot air oven.
Combination ovens combining the capability of microwave energy with the capability of radiant energy or circulated hot air are well-known in the art. Numerous forms of these ovens have appeared on the market and are available to the consumer at the retail level. In addition, several U.S. Patents have issued disclosing various aspects of these ovens. For example, U.S. Pat. No. 3,177,334 discloses an oven door window for an oven that is supplied with both microwave and radiant energy where the leakage of microwave energy through the window is deterred by a perforated plate that is an integral part of the door structure. U.S. Pat. No. 3,311,106 discloses a windowed oven door for use with high temperature ovens wherein the oven wall temperature may reach as high as 950.degree. to 1000.degree. F. U.S. Pat. Nos. 4,049,939 and 4,206,338 disclose a microwave and radiant window for oven doors wherein a microwave shield between glass panes is grounded at several points along the four sides of the window to dissipate microwave radiation. U.S. Pat. No. 4,211,910 discloses a door arrangement for a microwave and hot air oven having a glass plate member in front of and on the outer side of a shielding member for reducing leakage of microwave energy at the surface of the glass plate. All of these devices and references have sought to combine the convenience of having a window in an oven door to allow the user to monitor the progress of the cooking process with the additional design considerations involved with operating an oven that has a microwave or a self-cleaning capability.
Apart from these efforts to suppress the leakage of microwave or radiant energy from an oven door window, there have been efforts to suppress the leakage of these energies from the area between the main body of the oven and the oven door. The most notable of these seals is the choke-coupling type seal. Its major advantage lies in the fact that it does not rely on mechanical contact and the attendant problems of material deterioration for its sealing effectiveness. It does this by presenting a capacitive impedance at the opening to the choke cavity, thus establishing an E field. No H field can exist at the choke opening. Without an E cross H field, electromagnetic energy cannot be transmitted and, therefore, energy cannot leak from the oven.
U.S. Pat. No. 4,053,731 describes one such choke. Numerous others are described in U.S. Pat. No. 4,166,207. Yet, heretofore, no one has combined the advantages of the choke-coupling type seal with the convenience of a window in an oven door.